Relatives of people “executed” by the IRA for allegedly betraying the republican movement by acting as informers have begun legal action to discover the truth, as they prepare to tell their harrowing stories to an official investigation into at least 20 murders stretching back to the 1980s.

The revelation in April that Northern Ireland’s police ombudsman is conducting an investigation into whether the murders could have been prevented has triggered legal claims against the Ministry of Defence and the man identified as the army’s highest ranking agent in the IRA.

Detail of a mural on the corner of Falls Road, west Belfast, with an IRA warning for informers, in 1985. (Photograph: Kaveh Kazemi/Getty Images)

At the heart of the tortuous history of double-crossing is Freddie Scappaticci, known as Stakeknife, who fled Belfast after being unmasked as a senior IRA commander during a terrorist trial in 1991. Scappaticci was later identified as an agent for British military intelligence, but has consistently denied being Stakeknife.

For decades, the victims’ families – smeared by accusations of disloyalty and reluctant even after the end of the Troubles to talk to the police – were left alone with their grief and disbelief.

That their relatives may have been sacrificed to protect the army’s most productive agent – Stakeknife – inside the IRA’s Internal Security Unit, or “nutting squad”, has begun to emerge only recently.

The ombudsman’s office is investigating about 300 cases of alleged collusion. The key issue is whether double agents within the IRA were permitted to commit crimes – even murder – in order to gain the trust of paramilitary organisations or sacrifice IRA members to protect their own position.

Among the victims were:

• Joseph Mulhern, whose bullet-pierced body was discovered in a ditch beside a remote border crossing in County Tyrone. The IRA volunteer’s hands had been tied with wire. Three weeks later, in July 1993, his father was handed a tape of the 22-year-old supposedly confessing to informing on IRA activities.

• Caroline Moreland, 34, a single mother of three, was last seen alive ironing in her kitchen. Six weeks before the IRA announced its 1994 ceasefire, she was abducted, tortured and shot dead in County Fermanagh. The family received a recording in which she admitted betraying the location of a hidden IRA rifle.

• Paddy Trainor, 29, disappeared from a drinking club in February 1981. He was blindfolded before being shot in the back of the head; his body was marked by cigarette burns. His sister could not bear to listen to the cassette tape.

Weeks after burying his son, Frank Mulhern said, Scappaticci came up to him. “He shook my hand and asked how things were,” Mulhern said. “He was asking if anyone was giving me hassle.

“I knew he was with the nutting squad. He told me he had been up [in Donegal] where my son was being held. When he got there [Joseph] was only wearing a cross and chain – no clothes. He said my son looked really tired and ordered he be given a wash, a shave and something to wear.

Freddie Scappaticci - 'Stakeknife'

“Scappaticci knew about the two bullet wounds – to my son’s neck and head. I felt sick. Scap could have had me taken out and shot me if I did anything. He was a very powerful figure. If you were in the IRA and Scap was looking at you, your knees turned to water.”

The voice on the tape handed to the Mulhern family alternates between anxiety and resignation. Such recordings were meant to prove treachery but Joseph Mulhern’s statement was reminiscent of newsreel clips of a Stalinist show trial. In the confession, clearly extracted under duress, the young man introduces himself in a hesitant voice: “I’m a volunteer. My name is Joseph Mulhern. I’ve been working for the Special Branch this past three years.”

The tape stops and restarts several times. It ends in what sounds like a scripted plea: “I bitterly regret this past three years. I would urge anyone in this same predicament to come forward as there is no other way out.”

His father dismisses the recantation as fictitious. “I did not believe it,” Frank Mulhern said. “A few weeks earlier, Scappaticci had called around to see my son and had taken him to places where there were arms and explosives. The army later seized them.

“The IRA launched an investigation. The last two people to see the weapons had been Scap and my son. Obviously Scap did not fall under suspicion but my son did. His comrades in the IRA didn’t believe it. They all turned up for his funeral.” Some people nevertheless called his son a “tout” – slang for an informer.

Even after Stakeknife was exposed, the republican movement made no public apology. “The IRA will never admit anything,” Mulhern said. “They are like the British army; they are never wrong.”

He believes that, with an agent inside the IRA’s counter-intelligence unit, his son’s life could have been saved. “[Joseph] was held for two weeks, across the border. Why didn’t the handlers notify the Garda Síochána? They could have saved others’ lives, too. British intelligence was that far into the IRA, you wouldn’t know who was working for them.”

As evidence emerges, the scale of the security forces’ penetration of the province’s paramilitary organisations grows ever more astonishing. One informed source has estimated that by the end of the Troubles as many as 90% of loyalist and 50% of republican active paramilitaries had been recruited as informants.

The most thorough investigation into collusion, the De Silva report into the loyalist killing of the Belfast solicitor Patrick Finucane, published in December 2012, described agent-handling guidelines for the army’s Force Research Unit (FRU) – which controlled Stakeknife – as “contradictory”.

MI5, Special Branch and the FRU operated separate regimes, Sir Desmond de Silva said. “Agent-handlers and their superiors were expected to gather intelligence without clear guidance as to the extent to which their agents could become involved in criminal activity,” he concluded. “Intelligence officers were … asked to perform a task that, in some cases, could not be achieved effectively in ways that were lawful.”

Scappaticci was allegedly not the only agent operating inside the provisional IRA’s security department. Other names have surfaced. An informer who survived an IRA execution squad, Martin McGartland, has alleged two of the guards who held him were also from “a protected species”.

Kevin Winters, at the Belfast firm KRW Law, which is coordinating relatives’ compensation claims against Scappaticci and the Ministry of Defence, suspects the absence of a legal framework was deliberate. “De Silva confirmed that collusion as a state practice did exist,” he explained. “It showed there was no oversight, no protocols and the cynical view was that that allowed agents to thrive.

“By killing people at a low level in the organisation, they were ingratiating themselves into the paramilitary structure. The families of those shot dead as informers felt they were beyond victim status because of the stigma attached to the deaths. That has now changed.”

Shauna Moreland, 30, last saw her mother ironing in the family’s kitchen in west Belfast. “My mother had trained as a nurse so if anybody [in the IRA] was injured and couldn’t go to hospital, they would be brought to her,” Shauna recalled.

“I said ‘cheerio’. She gave me a hug and a kiss. I went off to my grandmother. She said ‘See you tomorrow’. She was missing for 15 days. They tortured her. I was first told it was a case of mistaken identity. I never felt the stigma because I was too young. Years later I found letters from IRA men in prison sending condolences; they knew it was an injustice.

“I want answers. I’ve listened to the tape they sent. It keeps stopping and starting. I don’t believe she did it. Why didn’t the police go and free her? [Stakeknife’s] handlers must have known. MI5 made the bullets and the IRA fired them. She was a sacrificial lamb.”

Her older brother, Marc Moreland, 34, understood more at the time. “I was heartbroken,” he remembers. “It was born into us that we were republicans. You hated the army, you hated Protestants, you hated the Brits. The IRA was meant to be on your side; they were meant to protect you.

“I went round to the house of a local IRA man after my mother was killed. He had steel security gates at the bottom of his stairs. I must have been 14 or 15. He wouldn’t come out but his son, who was 18, did. I [hit] him. The next day, four or five guys in balaclavas came round and told me to get out of the area.”

Eileen Hughes, 68, remembers snow falling the day the body of her brother, Paddy Trainor, was found. “My mother was in hysterics,” she said. “Another brother went to identify him. He said [Paddy] was covered in cigarette burns.

“He was shot to cover up for someone else. My brother listened to the tape. It was Paddy’s voice but we didn’t believe it. They accused him of being an informer. He had been lifted a few times by the police and may have got the price of a drink off them but he was not an informer.”

Hughes’s son, Tony Kane, was shot dead in 1995 by a republican group linked to the IRA, supposedly for drug dealing. She had been summoned to a meeting some time before at which, she said, Scappaticci told her: “The next complaint I get about your son, I will put one in his head.” She added: “I would like to see Scappaticci charged. I used to know him; my best friend used to go out with him. His father sold ice-creams around the area. I blame the police and the government. They knew these kids were getting shot to cover for [Stakeknife].”

The MoD declined to comment on the allegations. Lawyers for Scappaticci did not respond to requests for comment. Scappaticci’s whereabouts is unknown.

The dead have a habit of haunting Northern Irish politics. “If a truth and reconciliation process had been delivered years ago,” said Winters, “we wouldn’t have all this civil litigation. If the government had said: ‘Yes, we saved lives, but we got things wrong as well … ’ It’s the blanket denial that’s the problem. The families just want to know what happened.”

"Everyone, Republican or otherwise has their own particular part to play. No part is too great or too small, no one is too old or too young to do something."

~Bobby Sands 1954-1981~

'Mother Erin'

Two divine persons in one. A mother lamenting her children in bondage. A girl ravished by the Saxon, who weeps over her stringless harp. But her young champions keep watch in the mountains, awaiting the dawn of the bright sun of Freedom. They will gather around her with pikes and swords.